Metal sulfide initiators for metal oxide sorbent regeneration

ABSTRACT

A process of regenerating a sulfided sorbent is provided. According to the process of the invention, a substantial portion of the energy necessary to initiate the regeneration reaction is provided by the combustion of a particulate metal sulfide additive. In using the particulate metal sulfide additive, the oxygen-containing gas used to regenerate the sulfided sorbent can be fed to the regeneration zone without heating or at a lower temperature than used in conventional processes wherein the regeneration reaction is initiated only by heating the oxygen-containing. The particulate metal sulfide additive is preferably an inexpensive mineral ore such as iron pyrite which does not adversely affect the regeneration or corresponding desulfurization reactions. The invention further includes a sorbent composition comprising the particulate metal sulfide additive in admixture with an active metal oxide sorbent capable of removing one or more sulfur compounds from a sulfur-containing gas stream.

This invention was made with support from the United States Governmentunder Contract No. DE-AC21-88MC25006 awarded by the United StatesDepartment of Energy. The U.S. Government may have certain rights tothis invention.

FIELD OF THE INVENTION

The present invention relates to the desulfurization of a gas streamusing active metal oxide sorbents, and particularly to active metaloxide sorbents having enhanced regeneration properties and to enhancedmethods of regenerating active metal oxide sorbents.

BACKGROUND OF THE INVENTION

The removal of sulfur compounds from sulfur-containing gas streams is animportant environmental process. For this reason, various emissionrequirements limit the amount of sulfur compounds which can be emittedinto the atmosphere since sulfur compounds in gaseous emissions canresult in the pollution of the atmosphere which can produce undesirableresults such as acid rain and the like. Furthermore, in many cases whena gas stream containing sulfur contaminants is processed, the sulfurcompounds can poison sulfur sensitive catalysts, corrode equipment, orhave other adverse effects.

One technique for the desulfurization of sulfur-containing gas streamsinvolves heating the gas stream with particulate materials that absorbobjectional sulfur compounds. These sulfur absorbing materials or"sorbents" are typically high surface area, highly porous materialscapable of removing sufficient quantities of sulfur compounds so thatthe treated gas streams exhibit very low sulfur content and thus canmeet emission requirements for sulfur compounds. One conventional classof sorbents for absorbing sulfur compounds are active metal oxidesorbents which include supported and unsupported active metal oxidesderived from the calcination of various individual and mixed activemetal oxides.

For example, U.S. Pat. No. 4,088,736 to Courty et al. proposes a zincoxide sorbent which is supported on silica and/or alumina. Othersorbents for removing sulfur compounds that are derived from thecalcination of active metal oxides include the sorbents described inU.S. Pat. No. 4,769,045 to Grindley which proposes a zinc ferritesorbent prepared from the mixing and calcining equimolar amounts of zincoxide and iron oxide. U.S. Pat. Nos. 4,313,820 and 4,725,415, bothassigned to Phillips Petroleum Company, propose the use of zinc titanatesorbents formed from the mixing and calcination of zinc oxide andtitanium dioxide. U.S. Pat. No. 5,254,516 to Gupta et al. also discloseszinc titanate sorbents. Additionally, U.S. Pat. No. 4,977,123 toFlytzani-Stephanopolous et al., proposes a method of making mixed activemetal oxide sorbents prepared using calcined powders of oxides ofvarious metals such as for example, copper, iron, aluminum, zinc,titanium, and mixtures thereof to form the sorbent material.

One desirable application for active metal oxide sorbents is the removalof sulfur compounds from fuel gas streams. Specifically, active metaloxide sorbents are particularly desirable for use in the desulfurizationof coal gas streams that are used as fuel for power generation systems.These systems convert chemical energy stored in coal to electricity byfirst generating fuel gas via coal gasification, and then oxidizing thehot gas in either a turbine or a fuel cell. This approach, however, iscomplicated by the presence of sulfur in coal, which is converted toreduced sulfur species such as H₂ S, COS, and CS₂ during gasification.Subsequently, during combustion of the fuel gas, the H₂ S oxidizes toSO₂ which can cause the formation of acid rain if discharged into theatmosphere. In addition to environmental concerns, high concentrationsof H₂ S can be corrosive to energy producing equipment and can adverselyaffect the performance of molten carbonate fuel cells due to sulfurpoisoning of electrodes.

In the conventional method of removing sulfur compounds such as H₂ S,COS and CS₂ from coal gas streams, a hot gas stream is fed from thegasifier to an absorber at a temperature of between about 800° F. and1000° F. The absorber is typically a fixed-bed, fluidized bed, or movingbed reactor containing a particulate supported or unsupported activemetal oxide sorbent. The particles containing the active metal oxidesorbent are intimately contacted with the hot gas stream entering thereactor resulting in absorption of the sulfur compounds by the activemetal oxide sorbents, i.e., reaction of the active metal oxide andsulfur compound to form a metal sulfide (a sulfided sorbent) andtypically either water or carbon dioxide.

In the conventional desulfurization process, the metal sulfides derivedfrom the active metal oxide sorbents are recovered from thedesulfurization process and transported to an adiabatic bed reactor forregeneration. In the regenerator, the fluidizable particles containingthe sulfided sorbents are regenerated in an oxygen-containing gas streamsuch as an oxygen-enriched, a diluted, or an undiluted atmospheric airstream. The sulfided sorbent reacts exothermically with oxygen and isregenerated to the active metal oxide based sorbent and forms sulfurdioxide as a by-product.

In the regenerator, the temperature necessary to effectively initiatethe regeneration reaction is typically in excess of about 1000° F.Although part of the heat necessary to initiate the reaction is suppliedby the sulfided sorbent which, as described above, is heated to atypical temperature of between about 800° F. and 1000° F. during thedesulfurization process, the heat carried by the sorbent is generallybelow the temperature necessary for start up of the regenerationprocess. For example, conventional zinc oxide and zinc titanate sorbentstypically require a regeneration temperature in the range of betweenabout 1150° F. and 1400° F. Although various modifications have beenproposed to provide sorbents having somewhat lower initiationtemperatures for regeneration thereof, such modifications can lead tovarious other complications. Thus, for example, U.S. Pat. No. 5,439,867to Khare et al., and assigned to Phillips Petroleum, describes a zincoxide based sorbent containing a nickel oxide or nickel nitrate promoterwherein the sorbent is regenerated at temperatures of about 1100° F. and1200° F. However, the nickel promoter tends to increase disposalproblems associated with the spent sorbent, and during use of thesorbent for sulfur removal from fuel gas streams, also tends to catalyzethe formation of methane from carbon monoxide and hydrogen, whichdepletes the energy in the desulfurized fuel gas.

In any case, because the regeneration reactor is adiabatic, start up ofthe regeneration reaction is traditionally initiated by raising thetemperature of the oxygen-containing gas fed to the regenerator to atemperature above the initiation temperature of the regenerationreaction. However, heating of the oxygen-containing gas stream requiresincreased capital investment in various heating and associatedapparatus, and is also energy intensive and thus substantially increasesthe costs associated with sulfur removal from fuel gas streams.Moreover, in some cases, such as transport reactor-based processes,residence time of the sorbent in the regenerator may not be sufficientto provide the temperature rise needed to achieve regeneration ofsulfided sorbent.

SUMMARY OF THE INVENTION

The present invention provides sorbent compositions having enhancedregeneration properties, and methods for the enhanced regeneration ofsulfided sorbents. The compositions and methods of the invention canminimize or eliminate the need to rely on external energy for initiatingregeneration of a sulfided sorbent. This in turn, can significantlyreduce capital costs and process complexities associated with relianceon such external energy for initiation of sorbent regeneration.

The sorbent compositions of the invention comprise an active metal oxidesorbent in admixture with a particulate metal sulfide additive thatreacts exothermically with oxygen at a temperature below the temperaturenormally necessary for regenerating the sulfided sorbent with oxygen.The particulate metal sulfide additive exothermically reacts with oxygenduring the sorbent regeneration process to provide all or a portion ofthe activation energy necessary for initiation of sorbent regeneration.In turn, the oxygen-containing gas used for sorbent regenerationrequires no added heat, or less heating than in conventional processesin which the regeneration reaction is initiated only by the costlyprocess of increasing the temperature of the oxygen-containing gasstream. The particulate metal sulfide additive is preferably aninexpensive mineral ore such as iron pyrite which does not adverselyaffect the regeneration reaction or the corresponding desulfurizationreaction.

The particulate metal sulfide component is present in the sorbentcompositions of the invention in an amount less than the active metaloxide sorbent component and typically constitutes less than about 20 wt% of the sorbent composition, preferably less than about 10 wt % of thesorbent composition. The active metal oxide sorbent component isselected from various known compositions and can be present in any ofvarious known forms well known to the skilled artisan, including bothsupported and unsupported forms. Similarly, the particulate metalsulfide component can be supported or unsupported. Thus, the activemetal oxide sorbent and particulate metal sulfide additive can beprovided as an admixture supported on the same support material, oralternatively, the active metal oxide sorbent be provided on a firstparticulate support and the particulate metal sulfide additive providedon a second particulate support. In a preferred embodiment, theparticulate metal sulfide material is provided in the form ofunsupported particles, advantageously of fluidizable size and weight,which are simply mixed with the active metal oxide sorbent, which inturn, can be present in supported or unsupported form.

In use, the sorbent composition of the invention is contacted with asulfur containing gas stream in a desulfurization zone, which convertsthe active metal oxide sorbent to a sulfided sorbent but causes little,if any, significant change in the particulate metal sulfide additivebecause the particulate metal sulfide additive is substantially inertwith respect to the desulfurization process. The sulfided sorbent,together with the particulate metal sulfide additive, is recovered fromthe desulfurization zone and the mixture is passed to a regenerationzone for treatment with an oxygen-containing gas. In accord with theinvention, the quantity of external heat, if any, provided to theregeneration zone at start-up is insufficient to heat the sulfidedactive metal oxide sorbent to the temperature necessary to regeneratethe sorbent. However, the exothermic reaction of the oxygen-containinggas with the particulate metal sulfide additive releases sufficient heatto raise the temperature of the sulfided active metal oxide sorbent tothe initiation temperature necessary for regeneration. Advantageouslythe heat released by reaction of the particulate metal sulfide additiveis sufficient to raise the temperature of the regeneration zone by atleast 50° F.

The particulate metal sulfide additive provides useful energy forinitiation of the regeneration reaction without substantial negativeimpact on the regeneration process, or on the desulfurization process.Thus, no special equipment or process modifications are required in theregeneration zone to process the active metal oxide and sulfur dioxidegas by-products resulting from the reaction of the particulate metalsulfide additive with oxygen because conventional regeneration processesare already designed to process sulfur dioxide produced in theregeneration of sulfided sorbent. Furthermore, the particulate metalsulfide additives do not react detrimentally, if at all, with H₂ S orother sulfur components during the desulfurization process. The oxidizedparticulate metal sulfide additive, i.e., particulate metal oxide,formed in the regenerator can be recycled to the desulfurization processor, as in the case of preferred particulate metal sulfide additives suchas iron pyrite (FeS₂), can form a an attrition-prone ash-like material,that passes out of the regenerator with the sulfur dioxide-containing,regenerator off-gas.

In accordance with another aspect of the invention, the particulatemetal sulfide additive can be added to a sulfided, active metal oxidesorbent prior to, or during, regeneration of the sorbent, particularlyat start-up of the regeneration process. As in the above process, thesulfided sorbent and the particulate metal sulfide additive are treatedwith an oxygen-containing gas in the regeneration zone with or withoutthe addition of external heat. Reaction of the particulate metal sulfideadditive with oxygen increases the temperature of the regeneration zoneto the initiation temperature for the reaction of sulfided sorbent withoxygen, thus reducing or eliminating the need for heating theoxygen-containing gas fed to the regenerator.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings which form a portion of the original disclosure of thisapplication:

FIG. 1 is a schematic view of one preferred continuous desulfurizationand regeneration process according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the drawings and the following detailed description, preferredmethods and sorbent compositions of the invention are described indetail. Although the invention is described with reference to thesespecific preferred embodiments, it will be understood that the inventionis not limited to these preferred embodiments. But to the contrary, theinvention includes numerous alternatives, modifications and equivalentsas will become apparent from the consideration of the foregoingdiscussion and the following detailed description.

FIG. 1 illustrates a schematic view of a continuous desulfurization andregeneration process according to the invention. As shown in FIG. 1, theprocess includes a desulfurization zone 10 and a regeneration zone 20.In the preferred process of the invention illustrated in the drawing,both the desulfurization zone 10 and the regeneration zone 20 aredefined by fluidized bed reactors (including bubbling bed, circulatingbed, riser bed reactors, transport reactors and the like). It will beapparent to the skilled artisan, however, that sorbents and processes ofthe invention are equally applicable to other processes involvingdifferent types of reactors, including moving bed reactors and the like,as are described, for example, in Campbell, William M. and Henningsen,Gunnar B., Hot Gas Desulfurization Using Transport Reactors, publicationfrom the M. W. Kellogg Co., pp. 1059-64, 12th Annual InternationalPittsburgh Coal Conf. Proc.; September 1995 which is incorporated in itsentirety herein by reference.

As illustrated in FIG. 1, a sulfur-containing gas stream from an inlet22 is fed at a predetermined velocity into the desulfurization zone 10containing fluidizable particles 24 fed from an inlet hopper 26 orrecovered from the regeneration zone 20, through a regeneration inlet28. The term "fluidizable" as it is used herein refers to the ability ofthe particulate material to become hydrodynamically fluidized in a highvelocity gas stream (e.g. between about 5 and about 60 ft/s, preferablybetween about 10 and about 30 ft/s). Numerous factors contribute to thehydrodynamic properties of the particulate material including themorphology, size, shape, density, surface area and porosity of theparticulate material as is well known in the art. Typically, thedesulfurization zone 10 further includes a riser tube 29 which providesfurther contact between the fluidizable particles 24 and thesulfur-containing gas stream.

The sulfur-containing gas stream treated in the desulfurization zone 10contains at least one sulfur compound such as hydrogen sulfide, sulfurgas, sulfur dioxide, carbonyl sulfide (COS), carbon disulfide (CS₂), orthe like. Exemplary sulfur-containing gas streams include coal gasstreams which generally contain hydrogen sulfide, carbonyl sulfide andcarbon disulfide. The sulfur-containing coal gas stream typically entersthe desulfurization zone 10 after leaving a gasifier at a velocity ofbetween about 5 and about 60 ft/sec, preferably between about 10 andabout 30 ft/sec and at a temperature between about 600° F. and about1200° F., typically between about 800° F. and about 1100° F., but canexit the gasifier at lower or higher velocities and temperatures.

As stated above, the fluidizable particles 24 become fluidized in thesulfur-containing stream. The fluidizable particles 24, comprising thesorbent composition of the invention, include an active metal oxidesorbent component, and a particulate metal sulfide additive component inadmixture with the active metal oxide sorbent component. The particulatemetal sulfide additive is normally present in the admixture in an amountless than the active metal oxide sorbent. Typically, the initial amountof particulate metal sulfide additive is less than about 20 percent byweight, and preferably is less than about 10 percent by weight, based onthe total weight of the fluidizable particles 24. The exact amount ofthe particulate metal sulfide additive component will generally dependon the nature of the active metal oxide sorbent, the temperatureincrease desired in the regeneration zone 20, and the percentage ofoxygen in the oxygen-containing gas stream entering the regenerationzone.

The active metal oxide sorbent component comprises at least one activemetal oxide capable of removing one or more sulfur compound from thesulfur-containing gas stream. The term "active metal oxide sorbent" asused herein refers not only to active metal oxides but also to mixedactive metal oxides, including different oxides of the same elements,for example, zinc titanate which includes various oxides of the formulaZnO·n(TiO₂) and to mixed oxides of different metals, including activemetal oxides derived from the calcining of active metal oxides, and alsoto carbonates. Such active metal oxide sorbents can include binders thatare mixed or reacted with the active metal oxide, supports that supportthe active metal oxide, and the like, as will be well known to theskilled artisan. Active metal oxide sorbents exhibiting good absorptionrates and capacity for sulfur compounds, good regenerability withoutappreciable loss of efficacy or efficiency, and high attritionresistance are preferred for use in the invention.

Suitable active metal oxide sorbents include sorbents based on zincoxide, zinc titanate, zinc aluminate, zinc silicate, zinc ferrite, ironoxide, nickel oxide, manganese oxide, cerium oxide, copper oxide, coppercerium oxide, copper titanate, vanadium oxide, cobalt oxide, tungstenoxide, calcium oxide, calcium carbonate, magnesium oxide, magnesiumcarbonate, and mixtures thereof. The sorbent composition forming thefluidizable particles 24 can further include promoters or stabilizers ifdesired. Exemplary promoters and stabilizers include compoundscontaining cobalt, nickel, molybdenum, tungsten, platinum, ruthenium,zirconium, cerium, copper, and vanadium.

Preferred active metal oxide sorbents include zinc oxide-based sorbents(including zinc titanate sorbents) which can include binders, supports,promoters, stabilizers and small amounts (e.g., less than about 10%) ofother active metal oxides. Preferred zinc titanate sorbents typicallycontain both ZnO and TiO₂ in a suitable molar ratio typically rangingbetween 0.5 and 2.0. Other preferred active metal oxide sorbents includesupported zinc oxide sorbents.

Exemplary active metal oxide sorbents are disclosed in U.S. Pat. No.5,254,516, issued Oct. 19, 1993 to Gupta et al, which discloses zinctitanate sorbents having a particle size range of between 50 and 400microns prepared by granulating a mixture of fine zinc oxide andtitanium dioxide with an inorganic binder such as bentonite and/orkaolinite, and an organic binder, and then indurating the granules. Theresultant sorbent particles are highly attrition resistant and arecapable of absorbing significant quantities of sulfur compounds from afeed stream and are suitable for use in fixed bed, transport bed andfluidized bed reactors. Other exemplary active metal oxide sorbents aredisclosed in U.S. patent application Ser. No. 08/325,853 filed Oct. 19,1994, which is directed to highly uniform and attrition resistant zinctitanate particulate sorbent materials of high reactivity prepared byspray drying. Still other exemplary active metal oxide based sorbentsare disclosed in U.S. patent application Ser. No. 08/711,877, filed Sep.12, 1996, which discloses spherical fluidizable active metal oxidesorbents having attrition resistance and an increased particle sizeformed by spray drying a mixture of inorganic binder materials, anorganic binder and an active metal oxide such as zinc oxide. Still otherexemplary active metal oxide sorbents include Z-SORB III which is soldby Phillips Petroleum and contains a zinc oxide sorbent with a nickelpromoter.

The particulate metal sulfide additive included in the fluidizableparticles 24 can be in various forms including an essentially pure metalsulfide form, but is preferably in the form of a mineral ore. Suitablemineral ores include iron pyrite (FeS₂), alabandite (MnS), bornite (Cu₅FeS₄), braggite (PtS), chalcopyrite (CuFeS₂), covellite (CuS),chalcocite (Cu₂ S), marcasite (FeS₂), millerite (NiS), molybdenite(MoS₂), oldhamite (CoS), pyrrhotites (FeS), wurtzite/sphalerite (ZnS),digenite (Cu₉ S₅), cubanite (CuFe₂ S₃), argentite/acanthite (Ag₂ S), andpentlandite (Fe,Ni)₉ S₈ !! and mixtures thereof. Other sulfides such asarsenic, mercury, beryllium, bismuth, lead, antimony and cadmiumsulfides, and their naturally-occurring mineral ores are also capable offunctioning according to the invention but are less preferred because oftheir toxicity and corresponding disposal problems.

Preferably the particulate metal sulfide additive is present in the formof iron pyrite mineral ore, also known as pyrite or "fool's gold", whichgenerally includes on a weight basis 51.5% sulfur and 45.5% iron withthe remaining 3.0% being silica, copper, lead and other trace metals. Asis well known in the art, iron pyrite is a readily available,inexpensive mineral ore (approximately $200/ton) and is primarily usedin the production of sulfuric acid and in foundry, steel, abrasive,glass and battery applications.

The particulate metal sulfide additives, promoters and stabilizersselected for use in the present invention preferably do not reactadversely with, or catalyze undesirable reactions in, thesulfur-containing gas stream or the components thereof, to anysignificant extent. Furthermore, the particulate metal sulfideadditives, promoters and stabilizers used with the invention arepreferably non-hazardous and readily disposable. Therefore, nickel andnickel compounds are less preferred for use in the invention, especiallywith fuel streams, as they produce disposal problems and tend tocatalyze the formation of methane from carbon monoxide and hydrogen inthe sulfur-containing fuel streams. The formation of methane cansignificantly increase the temperature of the sulfur-containing fuelstream thus reducing the energy capacity of the fuel stream.Furthermore, eliminating the methane exotherm requires either acomplicated and expensive temperature control system, initiation ofregeneration at temperatures at which undesirable competing reactionsoccur, or presulfiding the sorbent as part of sorbent preparation.Because these solutions are not practical based on the current costprojections for successful commercialization of hot-gas desulfurization,the use of nickel compounds as promoters in fuel gas streams is lesspreferred.

Returning now to FIG. 1, in the desulfurization zone 10, the activemetal oxide sorbent reacts with the sulfur compounds from thesulfur-containing gas stream to form a metal sulfide (sulfided sorbent)and water or carbon dioxide thus removing the sulfur compounds from thegas stream. The desulfurization (absorption) reaction is typicallyinitiated at a temperature above about 600° F. and preferably less than1200° F., more preferably, a temperature between about 800° and about1100° F. The desulfurized gas stream and the fluidizable particles 24carried by the desulfurized gas stream flow from the riser tube 29 intoa solid-gas separator 30 such as a cyclone separator. From the solid-gasseparator 30, the fluidizable particles 24 are recovered and transportedto the regeneration zone 20 via suitable means such as pipe 32 and thedesulfurized gas stream exits through outlet 34.

The fluidizable particles 24 including sulfided sorbent and theparticulate metal sulfide additive are transported to the regenerationzone 20 and enter via inlet 36. An oxygen-containing gas stream from aninlet 38 is fed into the regeneration zone 20 at a velocity betweenabout 5 and about 60 ft/sec, preferably between about 10 and about 30ft/sec and fluidizes the fluidizable particles 24 to thereby facilitatecontact between the fluidizable particles and the oxygen-containing gasstream. The oxygen-containing gas stream used in the regeneration zonecan be, for example, a diluted, neat, or oxygen-enriched air stream(e.g., greater than 21% oxygen).

The heat carried by the heated sorbent particles, the particulate metalsulfide additive, and the heat added to the oxygen-containing stream, ifany, are sufficient to establish conditions in the regeneration zone 20for initiating reaction of the metal sulfide additive with oxygen in ahighly exothermic combustion reaction to form a metal oxide and sulfurdioxide (typically a temperature at or above 800° F.). In turn, the heatreleased by this reaction increases the temperature in the regeneratorto a temperature sufficient to initiate the desired self-sustainingcombustion/regeneration reaction of the sulfided sorbent.

Those skilled in the art will understand that regeneration of thesulfided sorbent can be complete or incomplete, i.e., substantiallycomplete conversion of the sulfided sorbent to the active metal oxidestate, or conversion of only a portion of the sulfided sorbent to theactive metal oxide state. In many cases it is desirable to achievecomplete regeneration of the sulfided sorbent. However in other cases,it is desirable to remove only a portion of the sulfur from the sulfidedsorbent, so that a portion of the sorbent is recirculated in a partiallysulfided state. The degree of regeneration can be controlled bycontrolling the temperature conditions, oxygen content, and sorbentresidence time in the regenerator as is known in the art.

Accordingly, the particulate metal sulfide additive used in the presentinvention can be used to promote complete regeneration of the sulfidedsorbent when the temperature conditions in the regenerator would nototherwise support the self-sustaining regeneration of the sulfidedsorbent. Alternatively the particulate metal sulfide additive can beused to increase the extent of sorbent regeneration in the regeneratorto the desired extent of regeneration, while minimizing the use ofexternal energy sources for heating of the regeneration gas stream.Accordingly, the term, "conditions sufficient to initiate regeneration",and variations thereof, is used herein to include conditions sufficientto initiate complete regeneration, or sufficient to increase the extentof regeneration of the sulfided sorbent to a desired amount.

Because the regeneration zone 20 is adiabatic, the temperature of theregeneration zone will stabilize at steady state conditions as a resultof the combustion of the particulate metal sulfide additive and theexothermic reaction of the sulfided sorbent with oxygen. Typically, thetemperature of the regeneration zone 20 can increase between start-upand steady state conditions, from an initial temperature of betweenabout 650° F. and 1050° F. to a temperature of between about 1100° F.and 1500° F. as the regeneration zone reaches steady-state.

Preferably, a sufficient amount of the particulate metal sulfideadditive is present in the regeneration zone 20 to raise the temperatureof the regeneration zone by at least 50° F., and typically the quantityof particulate metal sulfide additive is sufficient to raise thetemperature of the regeneration zone by greater than about 100° F.Temperature increases of 500° F. or more can be achieved by theparticulate metal sulfide additives used in the present invention.

As stated above, the particulate metal sulfide additive reacts withoxygen to form a metal oxide and sulfur dioxide at temperaturesgenerally below the temperatures which initiate the regeneration of thesulfided sorbent. Because conventional regeneration processes arealready designed to process sulfur dioxide produced in the regenerationof sulfided sorbent, no special equipment or procedures are needed inthe regeneration zone 20 to process the gas by-products resulting fromthe combustion of the particulate metal sulfide additive. Furthermore,the particulate metal sulfide additives generally do not react with H₂ Sduring coal gas desulfurization. Although the CO and/or H₂ present inthe coal gas may partially reduce the particulate metal sulfide additiveproducing some H₂ S and a mixed stoichiometric sulfide, this reaction isnot detrimental to the desulfurization process.

In Table 1 below, the combustion (oxidation) reactions and the heats ofreaction and Gibbs free energy are listed for exemplary metal sulfidesin their naturally occurring mineral forms, as can be used in theinvention.

                                      TABLE 1    __________________________________________________________________________    Naturally-Occurring Metal Sulfide Compounds               Approximate              Thermodynamic Properties at                                        500° C.               Chemical                 (932° F.)    Natural Mineral Ore               Formula                      Proposed Oxidation Reaction                                        ΔH (KCal)/mol                                                  ΔG (KCal)/mol    __________________________________________________________________________                                                  O.sub.2    Alabandite MnS    MnS + 1.5O.sub.2 = MnO + SO.sub.2                                        -74.80    -64.70    Bornite    Cu.sub.5 FeS.sub.4                      Cu.sub.5 FeS.sub.4 + 7O.sub.2 = FeO + 5CuO                                        -64.41sub.2                                                  -48.99    Braggite   PtS    PtS + 1.5O.sub.2 = PtO + SO.sub.2                                        -45.28    -38.22    Chalcopyrite               CuFeS.sub.2                      CuFeS.sub.2 + 3O.sub.2 = CuO + FeO + 2SO.sub.2                                        -66.68    -57.33    Covellite  CuS    CuS + 1.5O.sub.2 = CuO + SO.sub.2                                        -63.85    -53.24    Chalcocite Cu.sub.2 S                      Cu.sub.2 S + 2O.sub.2 = 2CuO + SO.sub.2                                        -64.14    -44.35    Iron pyrite/Marcasite               FeS.sub.2                      FeS.sub.2 + 2.5O.sub.2 = FeO + 2SO.sub.2                                        -66.55    -65.59    Millerite  NiS    NiS + 1.5O.sub.2 = NiO + SO.sub.2                                        -72.50    -62.09    Molybdenite               MoS.sub.2                      MoS.sub.2 + 3.5O.sub.2 = MoO.sub.3 + 2SO.sub.2                                        -72.61    -61.55    Oldhamite  CaS    CaS + 1.5O.sub.2 = CaO + SO.sub.2                                        -73.29    -63.28    Pyrrhotite FeS    FeS + 1.5O.sub.2 = FeO + SO.sub.2                                        -75.84    -66.14    Wurtzite/Sphalerite               ZnS    ZnS + 1.5O.sub.2 = ZnO + SO.sub.2                                        -71.41    -61.64    __________________________________________________________________________

The heats of reaction in the above table demonstrate that a highlyexothermic reaction results in the combustion of the particulate metalsulfide additives. Furthermore, the Gibbs free energy values for thereaction indicate high combustibility of the particulate metal sulfideadditives.

The metal oxide resulting from the oxidation of the particulate metalsulfide additive can be recycled in the process or, as in the case ofiron pyrite (FeS₂), can form a lightweight solid material such as an ashwhich is not recycled. As illustrated in FIG. 1, the oxygen-containinggas stream and the fluidizable particles 24 carried by theoxygen-containing gas stream flow from the regeneration zone 20 into ariser tube 39 which further facilitates contact between the fluidizableparticles and the oxygen-containing gas stream. The fluidizableparticles 24 and oxygen-containing gas stream then advance to asolid-gas separator 40 such as a cyclone separator. From the solid-gasseparator 40, the fluidizable particles 24 are recovered and returned tothe desulfurization zone 10 via suitable means such as pipe 42 and theoxygen-containing gas stream, which now contains significant amounts ofSO₂, exits through outlet 44 for further treatment. In the case of ironpyrite, and similar additives, a portion of the metal oxides derivedfrom the particulate metal sulfide additive is not recovered by thesolid-gas separator and exits through outlet 44 with the off-gas stream.Loss of these metal oxides particularly occurs when the metal oxides areconverted to an ash-like form. Furthermore, a portion of the activemetal oxide sorbent is normally lost due to attrition through outlet 44in the same manner as the metal oxide derived from the particulate metalsulfide additive.

As shown in FIG. 1, a substantial portion of the fluidizable particles24 including the regenerated active metal oxide sorbent, are recoveredfrom the regeneration zone 20 and returned to the desulfurization zone10 through pipe 42 and inlet 28. The fluidizable particles 24 returnedto the desulfurization zone 10 typically include, in addition to theregenerated sorbent, at least minor amounts of sulfided sorbent andparticulate metal sulfide additive, and particulate metal oxides derivedfrom the particulate metal sulfide additive. The fluidizable particles24 and, in particular, the regenerated sorbent, are then combined with asulfur-containing gas in the desulfurization zone 10 as described above.The process is therefore continuous and the active metal oxide sorbentis continually sulfided by absorbing sulfur compounds in thedesulfurization zone 10 and regenerated in the regeneration zone 20.

Because a portion of the active metal oxide sorbent is continuously lostfrom the process due to attrition, additional active metal oxide sorbentis typically continuously added to the desulfurization zone 10 throughinlet hopper 26 to maintain enough of the active metal oxide sorbent tosufficiently remove the sulfur compounds from the sulfur-containing gasstream fed into the desulfurization zone. In one preferred embodiment ofthe invention, the particulate metal sulfide additive is alsocontinuously added to the desulfurization zone 20 together with thefresh sorbent via hopper 26. The particulate metal sulfide additive,when continuously added in this manner, continuously promotes atemperature increase in the regenerator to provide sufficient heat toincrease the degree of sorbent regeneration in the regenerator to thedesired degree of regeneration, or to provide sufficient heat to providea self-sustaining regeneration reaction of the desired degree in theregenerator when the temperature conditions in the regenerator would nototherwise support a self-sustaining regeneration of the sorbent to anysignificant extent.

In some cases it is not necessary to add additional particulate metalsulfide additive following start-up of the process in order to establishregeneration conditions or to increase the degree of regeneration. Insuch cases the benefit of the particulate metal sulfide additive isrealized during startup of the regeneration process. Thus, in the caseof some process designs, once the temperature of the regeneration zone20 is raised to the initiation temperature of the regeneration reactionby the combustion of the particulate metal sulfide additive, theparticulate metal sulfide additive is generally no longer needed toincrease the temperature of the regeneration zone 20, primarily becausethe regeneration reaction is exothermic and the regeneration zone 20 isadiabatic.

As indicated previously, the sorbent composition of the inventioncomprising the particulate metal sulfide additive and the active metaloxide sorbent can be provided in numerous different forms. In any case,the metal sulfide is present in a particulate form that is physicallydistinct from the active metal oxide used in the sorbent composition.This allows the particulate metal sulfide additive to be used in itsnaturally-occurring mineral form in the preferred embodiments of theinvention, and in any case allows the particulate metal sulfide additiveto be present in the form of a sulfide, distinct from the sorbent metalwhich must be in oxide form to function as a sorbent.

The sorbent composition and particulate metal sulfide additive can beprovided in admixture in numerous different forms or arrangements. Inone embodiment, the active metal oxide sorbent and particulate metalsulfide additive can be supported together on the same particulatesupport material. Suitable particulate support materials are generallyinert with respect to the desulfurization and regeneration processes andinclude titania, alumina, silica, kaolin, emathlite, chromia, andmixtures thereof. The active metal oxide sorbent and the particulatemetal sulfide can be mixed and applied together to the particulatesupport material by granulation, spray-drying or other suitabletechniques well known to one skilled in the art, or the active metaloxide can be chemically deposited on the support and thereafter theparticulate metal sulfide additive can be physically deposited on thesupport.

In preferred sorbent compositions of the invention, the active metaloxide sorbent and the particulate metal sulfide additive are provided asfluidizable particles. Preferred fluidizable active metal oxide sorbentsare disclosed in U.S. Pat. No. 5,254,516 to Gupta et al., in commonlyassigned U.S. application Ser. No. 08/325,853 to Gupta et al. filed Oct.19, 1994 and in commonly assigned U.S. application Ser. No. 08/711,877to Gupta et al, filed Sep. 12, 1996. These applications and the Gupta etal. patent are incorporated herein by reference in their entirety. Inthe case of fluidizable sorbents wherein the metal sulfide particles areunsupported, the particulate metal sulfide additive is ground orotherwise sized to a fluidizable size having hydrodynamic propertiessubstantially the same, or generally comparable to the fluidizablesorbent. The hydrodymanic properties depend on particle size, sphericityand particle density, as is well known in the art.

The metal sulfide can alternatively be provided on a particulate supportmaterial separate from the active metal oxide sorbent. This isparticularly preferred when the regeneration zone is a moving bedreactor. In such case, although the active metal oxide sorbent and theparticulate metal sulfide additive are applied on separate particles ofthe support material, the particulate support material used for both theactive metal oxide sorbent and the particulate metal sulfide additivecan be identical. Thus, the metal sulfide can be applied to a support asdescribed previously, but it is not mixed with the active metal oxide onthe same support material.

In one advantageous embodiment, the particulate metal sulfide additiveis provided in the form of fluidizable or non-fluidizable pellets orparticles comprising added binder material. These pellets can be formedby any suitable pellet-making techniques known in the art including diskpelletization, extrusion/spheronization, pellet presses, and the like.For example, the metal sulfide particulate matter can be mixed withvarious organic and/or inorganic binders, and/or other inert materials,the mixture formed into a paste in water or an organic solvent, and thepellets formed by extrusion, spheronization and drying.

Another alternative for preparing the sorbent composition of theinvention, is to provide the active metal oxide sorbent on a firstparticulate support material as described above and to provide theparticulate metal sulfide additive as fluidizable particles mixed withthe supported active metal oxide sorbent. This particular alternative ispreferred with fluidized bed reactors and does not require theadditional step of applying the metal sulfide to a support material. Themetal sulfide particles are typically spherical and prepared to have thedesired morphology, size, shape, density, porosity, surface area, etc.,to become fluidized in the desulfurization and regeneration zones, 10and 20. Preferably, the supported active metal oxide sorbents and theparticulate metal sulfide additive are provided and mixed such that thehydrodynamic properties of the sorbent composition are uniform.

As indicated previously, the process of the invention can be conductedwithout any premixing of the particulate metal sulfide additive and theactive metal oxide sorbent. In such instances, the particulate metalsulfide additive can be added directly to the desulfurization zone, orto the sulfided active metal oxide sorbent just prior to, or during,regeneration of the sorbent. As in the above described processes, thesulfided sorbent and the particulate metal sulfide additive are treatedwith an oxygen-containing gas in the regeneration zone under conditionssufficient to initiate reaction of the particulate metal sulfideadditive with oxygen and to increase the temperature of the regenerationzone to a temperature sufficient for initiation of the regenerationreaction of sulfided sorbent with oxygen.

In many cases, it is highly desirable to add additional fresh make-upmetal sulfide additive continuously or intermittently to thedesulfurization/regeneration reaction system in order to replenishadditive that is continuously lost from the system. Regeneration of theparticulate metal sulfide additive, particularly when present in itspreferred embodiment as a naturally-occurring mineral, will generallyprovide a highly attrition-prone ash-like material. In such cases theability of metal sulfide additive to produce the desired temperaturerise during regeneration decreases with each subsequent desulfurizationand regeneration cycle since the ash-like material is not recycled tothe desulfurizer. When the metal sulfide additive experiences highattrition, more active metal oxide material can be added to thedesulfurization/regeneration reaction on a continuous basis.Alternatively, fresh metal sulfide additive can be added to provide anynecessary temperature rise as fresh metal sulfide additive, particularlyin its naturally-occurring mineral form, is quite inexpensive and can befed along with the active metal oxide sorbent.

The invention will now be further described by the followingnon-limiting examples. In these examples, a 2.5-kg batch of iron pyrite(CAS # 12068-85-8) having a particle size range of 85 percent below 50mesh was purchased from E. M. Science Company and used as theparticulate metal sulfide additive. Tests were conducted using CMP-107sorbent, a zinc titanate sorbent, the preparation of which is describedin U.S. patent application Ser. No. 08/711,877, filed Sep. 12, 1996 byRaghubir Gupta for transport reactor applications, with and without theiron pyrite. These tests were conducted in the high-temperature,high-pressure (HTHP) bench-scale sorbent test facility described inGupta, R. P. and Gangwal S. K., Enhanced Durability of DesulfurizationSorbents for Fluidized-Bed Applications, NTIS Report No.DOE/MC/25006-3271 (DE93000247), November, 1992, which is incorporated inits entirety herein by reference.

The following examples describe regeneration processes using mixedsorbent materials as described above. In the following examples, it wasgenerally found that following the introduction of an O₂ -containing gasstream into the reactor at 900° F., SO₂ concentration in the reactoreffluent would begin to rise rapidly. After a certain lag timeassociated with placement of the thermocouple, the temperature wouldalso begin to rise rapidly. With the correct combination of O₂ in thefeed and additive content in the sorbent bed, the temperature increasewould be sufficient to initiate regeneration of the mixed-active metaloxide sorbent. Temperature increases of 200° F. to 500° F. wereobserved, although some of this temperature increase was a result of theregeneration of the sulfided mixed-active metal oxide sorbent.

EXAMPLE 1

(COMPARATIVE)

A 200 g sample of zinc titanate sorbent labeled CMP-107 with particlesbetween 20 and 150 μm was loaded in the HTHP reactor. No particulatemetal sulfide additive was added with the sorbent material. At 280 psigand 900° F., the CMP-107 material was sulfided in a 2-in I.D. reactorwith 12.7 standard liters per minute (SLPM) of simulated Texaco coalgas. The composition of the simulated Texaco coal gas was 2 vol % H₂ S,30 vol % CO, 10 vol % CO₂, 20 vol % H₂, 18 vol % N₂, and 20 vol % steam.The exposure of the simulated coal gas continued until the H₂ Sconcentration in the reactor effluent exceeded 1000 ppmv. After a 30minute nitrogen purge to remove all traces of coal gas, the pressure wasreduced to 100 psig. Regeneration of the sulfided sample was attemptedat 900° F. with 4 SLPM of air. After the oxygen concentration in theeffluent became essentially the same as the feed, the regenerationtemperature was increased approximately 20° F. At 920° F., nosignificant regeneration was observed. The regeneration temperature wasrepeatedly increased by about 20° F. until regeneration initiation wasobserved. At 1140° F., initiation of the regeneration reaction wasobserved with the associated rapid rise in SO₂ concentration andtemperature increase associated with the exothermic oxidation of thesulfided sorbent. The maximum temperature observed during regenerationwas 1370° F. The SO₂ concentration peaked at 10.5 vol %. Regenerationlasted for 130 minutes. However, the SO₂ concentration was below 2000ppmv after 102 minutes.

EXAMPLE 2

(INVENTION)

A 200 g sample of CMP-107 containing particles of between 20 and 150 μmwas mixed with 10 g of iron pyrite (5 wt. %) having particles between 53and 75 μm. This mixture was loaded in the HTHP reactor system. At 900°F. at 280 psig, this mixture was sulfided with 12.7 SLPM of simulatedTexaco coal gas. The simulated Texaco coal gas contained 2 vol % H₂ S,30 vol % CO, 10 vol % CO₂, 20 vol % H₂, 18 vol % N₂ and 20 vol % steam.Exposure to simulated coal gas with H₂ S continued until the H₂ Sconcentration in the reactor effluent exceeded 1000 ppmv. After a 30minute nitrogen purge to remove all traces of coal gas, the pressure wasreduced to 100 psig. Regeneration of the sorbent mixture was started at940° F. in 4 SLPM of neat air. The SO₂ concentration and temperaturebegan to rapidly increase. The SO₂ concentration increased to about 8vol %. The maximum observed temperature was 1500° F. Regeneration lastedfor 32 minutes with the SO₂ concentration exceeding 2000 ppmv for 30minutes.

EXAMPLE 3

(INVENTION)

This example demonstrates the impact of iron pyrite additive over threecycles of use.

Another 200 g of CMP-107 with particles between 20 and 150 μm and 10 gof iron pyrite with particles between 53 and 75 μm were mixed and loadedinto the HTHP reactor system. This mixture was sulfided at 900° F. and280 psig with simulated Texaco coal gas. The simulated Texaco coal gascontained 2 vol % H₂ S, 30 vol % CO, 10 vol % CO₂, 20 vol % H₂, 18 vol %N₂ and 20 vol % steam. Exposure to simulated coal gas with H₂ Scontinued until the H₂ S concentration in the reactor effluent exceeded1000 ppmv. After a 30 minute nitrogen purge to remove all traces of coalgas, the pressure was reduced to 100 psig. Regeneration of the sorbentmixture was started at 920° F. in 4 SLPM of neat air. The temperatureand SO₂ began to rapidly increase after the introduction of air. Themaximum temperature observed during regeneration was 1370° F. Themaximum SO₂ concentration was about 8 vol %. The regeneration lasted for80 minutes with the SO₂ concentration exceeding 2000 ppmv for 60minutes.

After this regeneration, the reactor was purged with nitrogen andpressure increased to 280 psig. The mixture was sulfided a second timeusing the same simulated Texaco coal gas with 2 vol % H₂ S at 12.7 SLPM.After the H₂ S concentration in the reactor effluent reached 1000 ppmvthe sulfidation was terminated. The reactor system was purged for 30minutes before reducing the pressure to 100 psig. Regeneration wasstarted at 920° F. by introducing 4 SLPM of neat air. Sorbenttemperature and SO₂ rapidly increased. The sorbent bed reached a maximumtemperature of 1370° F. The SO₂ concentration peaked at 8.5 vol %. Theregeneration lasted for 70 minutes with the SO₂ concentration exceeding2000 ppmv for 55 minutes.

After a 30 minute purge in nitrogen, a third sulfidation of thismaterial was performed at exactly the same conditions as used in theprevious cycle. After a 30 minute nitrogen purge, a third regenerationwas performed at 920° F. with 4 SLPM of neat air at 100 psig. Themaximum sorbent temperature during this third regeneration was 1230° F.The SO₂ concentration peaked at 7.4 vol %. Total run time for theregeneration was 110 minutes with the SO₂ concentration being above 2000ppmv for about 75 minutes.

EXAMPLE 4

(INVENTION)

This example demonstrates the applicability of metal sulfide additivewith a spray dried zinc titanate sorbent (having different chemicalcomposition than CMP-107) developed by a different vendor usingdifferent set of binders and support materials.

A 200 g sample of an attrition-resistant zinc titanate sorbent labeledEX-S03 with particles between 50 and 150 μm was physically mixed with 10g of iron pyrite with particles between 53 and 75 μm. This mixture wasloaded in the HTHP reactor system. At 1000° F. and 262 psig, the mixturewas sulfided with 30 SLPM of simulated coal gas containing 15 vol % H₂,25 vol % CO, 5 vol % CO₂, 5 vol % H₂ O, 1.4 vol % CH₄, 48.4 vol % N₂,and 0.2 vol % H₂ S. Exposure to simulated coal gas with H₂ S continueduntil the H₂ S concentration in the reactor effluent exceeded 1000 ppmv.After a 30 minute nitrogen purge to remove all traces of coal gas,regeneration of the sorbent was started by heating the sorbent to 1040°F. at 262 psig with 10 SLPM of neat air. The temperature of the reactionand the SO₂ concentration in the off gases were monitored throughoutregeneration. It was found that initially, both the SO₂ concentration,and temperature, increased rapidly and then stabilized. The maximum SO₂concentration measured during regeneration was 15 vol %, whereas themaximum observed temperature was 1450° F. Regeneration lasted for 40minutes.

The above sulfidation-regeneration sequence was continued for 10-cycles.No additional iron pyrite particles were added during this period.During the first four cycles, the iron pyrite particles provided enoughtemperature rise during regeneration to allow initiation of theregeneration of sulfided zinc titanate at 1040° F. During Cycles 5 to10, regenerations had to be started by heating to the higher temperatureof 1110° F., indicating that pyrites were transformed into otherchemical forms.

EXAMPLE 5

(INVENTION)

This example demonstrates the applicability of the iron pyrite additivein a pilot-scale hot-gas desulfurization system.

Approximately 15 lbs of the same sorbent used in Example 4 (EX-S03)containing particles between 50 and 150 μm, and 1.5 lb of iron pyriteparticles ranging in size from 0 to 40 μm were loaded in M. W. Kellogg'sTransport Reactor Test Facility (TRTU). This pilot-scale test facilityhad a riser section that was about 40-ft. tall and was operated atvelocities in 10 to 20 ft/s. This facility is a prototype of acommercial system shown in FIG. 1.

Using a gas velocity of 10 to 20 ft/s and a very dilute gas-solidsuspension of a density in the range of 1 to 3 lbs per cu.ft., thissorbent reduced the H₂ S level of coal gas from 12,000 ppmv to less than1000 ppmv within a residence time of about 3 sec at a temperature in therange of 1000 to 1,200° F. and 100 psi pressure. The sulfided sorbentwas regenerated with neat air in this transport reactor system. Theregeneration was successfully carried out at 1020° F. with about 200° F.temperature rise provided by iron pyrites (see Example 6, below).

EXAMPLE 6

(COMPARATIVE)

The EX-S03 sorbent was tested in TRTU exactly in the same manner asExample 5, except for that no iron pyrite particles were added. Theminimum temperature at which the sorbent supported a self-sustainingregeneration was 1200° F. At lower temperatures, an instant oxygenbreakthrough was observed indicating a lack of regeneration.

EXAMPLE 7

(INVENTION)

This example describes the preparation of the metal sulfide additives ofthe invention in the form of 4 mm iron pyrite pellets without anysupport and with titania, alumina and emathlite as support materials.

All materials described in this example were prepared by the followingprocedure. The dry material was charged into a conventional kneaderdevice and the motor started. Dry mixing was conducted for 2 to 5minutes. After dry mixing, liquid carboxymethylcellulose binder wasslowly charged into the moving dry powder. Movement of the two "S"shaped kneading arms caused intimate mixing of the charged materials.When the mixing sample was homogeneous, it was dumped into trays andloaded onto the feed pan of an extruding apparatus (EXDFS-100-XTRUDER®).Twin auger blades transported the wet powder from the feed hopper ontothe extrusion blades. The extrusion blades wiped material through thedie plate, forming cylindrical extrudates. A measured amount of theextruded material was loaded a commercially available pelletizingdevice, (MARUMERIZER QJ-400) in which the extruded particles were brokenand rounded by impact forces. When the material reached the desiredshape, a discharge port was opened allowing the spheres into acontainer. All samples were placed in an oven and dried at 120° C. for aminimum of 2 hr.

The relative compositions and crush strength data for the different typeof pellets made is provided in the following table.

    ______________________________________    Sample Label               A      B      C    D    E    F    G    ______________________________________    Material (wt %)    Emathlite  80     20    Titania                  20   80    Alumina                            20   80    Pyrite     20     80     80   20   80   20   >90    Binder     M.sup.1                      M.sup.1                             M.sup.1                                  M.sup.1                                       M.sup.1                                            M.sup.1                                                 M.sup.1    Crush Strength               7.66   12.71  11.81                                  6.61 9.87 12.10                                                 8.27    (lb.sub.f /pellet)    ______________________________________     M.sup.1 refers to Methocel.

EXAMPLE 8

(INVENTION)

This example demonstrates the stability of the pellets produced inExample 7 throughout several sulfidation and regeneration cycles. A 400g batch of 4 mm diameter pellets of Sample A, prepared as described inExample 7, was loaded in the HTHP reactor system. After heating thereactor to 750° F. in nitrogen, the sample was exposed to 12 SLPM of 5vol % O₂ in nitrogen at 88 psig. Both the temperature of the additivebed and the SO₂ in the reactor effluent increased rapidly. The maximumSO₂ concentration observed was 2.5 vol %, whereas the maximumtemperature in the additive bed was 1030° F.

After regeneration, the reactor spurged withpurged with nitrogen for 30minutes and the pressure increased to 280 psig. The additive wassulfided with a simulated Texaco coal gas containing 2 vol % H₂ S, 30vol % CO, 10 vol % CO₂, 20 vol % H₂, 18 vol % N₂ and 18 vol %. steam anda flowrate of 12 SLPM. Exposure to simulated coal gas with H₂ Scontinued until the H₂ S concentration in the reactor effluent exceeded1000 ppmv. The reactor system was purged with nitrogen for 30 minutesbefore reducing the pressure to 88 psig. The second regeneration wasstarted at 900° F. with 12 SLPM of 5 vol % O₂ in nitrogen. The SO₂concentration and temperature both began to rise. The reactor effluentSO₂ concentration reached its maximum value at 2.1 vol %. The maximumtemperature observed was 1010° F.

EXAMPLE 9

(COMPARATIVE)

A 400 g sample of 4 mm diameter zinc titanate sorbent pellets was loadedin the HTHP reactor system. This sample was sulfided at 900° F., 280psig and 9.6 SLPM of simulated Texaco coal gas containing 2 vol % H₂ S,30 vol % CO, 10 vol % CO₂, 20 vol % H₂, 18 vol % N₂ and 18 vol % steam.Exposure to simulated coal gas containing H₂ S was continued for 125minutes. The reactor was purged with nitrogen for 30 minutes beforereducing the pressure to 88 psig. Regeneration was started at 1000° F.and 4.8 SLPM of 7 vol % O₂ in nitrogen. The temperature in the sorbentbed increased to a maximum temperature of 1035° F. The maximum reactoreffluent SO₂ concentration was 3.4 vol %.

EXAMPLE 10

(INVENTION)

This example demonstrates the use of the additive materials prepared inExample 7 to enhance the regeneration process of Example 9. A 268 gsample of a 4 mm diameter pre-sulfided zinc titanate sorbent pellets wasmixed with 26 g (10 wt %) of Sample F pellets prepared as described inExample 7. This mixture was loaded in the HTHP reactor system. Afterheating the reactor to 900° F. and increasing the pressure to 88 psig,the mixture was exposed to 2.8 SLPM of 5 vol % O₂ in nitrogen. Theseconditions were sufficient to initiate a self-sustaining regeneration.The maximum temperature recorded in the sorbent bed was 1010° F. Themaximum SO₂ concentration in the reactor effluent was 2.0 vol %.

Accordingly it can be seen that the invention provides an inexpensivealternative to conventional methods of regenerating sulfided sorbentsused in the removal of sulfur compounds. The method of the inventionuses the combustion of a metal sulfide compound to increase thetemperature in a regeneration zone to above the initiation temperatureof the regeneration reaction of the sulfided sorbent. The metal sulfidemay be in the form of an inexpensive mineral ore and thus there islittle expense associated with increasing the temperature in theregeneration zone. Furthermore, the metal sulfide is preferably inertwith respect to the contents of the sulfur-containing gas stream andreadily oxidizes to form an active metal oxide which may be recycled inthe process or lost due to attrition.

The invention has been described in considerable detail with referenceto its preferred embodiments. However, as indicated previously, thesemethods and compositions of matter described herein are susceptible tonumerous alternatives and variations without departure from the spiritand scope of the invention as described in detail in the foregoingspecification and defined in the appended claims.

That which is claimed is:
 1. A process of regenerating an active metaloxide sorbent used for removing at least one sulfur compound from asulfur-containing feed stream comprising the steps of:recovering asulfided active metal oxide sorbent from a desulfurization zone; andtreating the sulfided sorbent with an oxygen-containing gas stream in aregeneration zone in the presence of a particulate metal sulfideadditive under conditions sufficient to provide an exothermic reactionbetween oxygen and the particulate metal sulfide additive to therebyraise the temperature of the regeneration zone by at least 50° F. andinitiate regeneration of the sulfided sorbent.
 2. The process accordingto claim 1 further comprising the step prior to said recovering step,of;contacting a sulfur-containing feed stream with an admixture ofactive metal oxide sorbent and the particulate metal sulfide additive insaid desulfurization zone at a temperature sufficient to allow theactive metal oxide sorbent to react with at least one sulfur compoundfrom the sulfur-containing feed stream to form sulfided sorbent.
 3. Theprocess according to claim 1 wherein said particulate metal sulfideadditive comprises a mineral ore selected from the group consisting ofiron pyrite, alabandite, bornite, braggite, chalcopyrite, covellite,chalcocite, marcasite, millerite, molybdenite, oldhamite, pyrrhotites,wurtzite/sphalerite, digenite, cubanite, argentite/acanthite, andpentlandite, and mixtures thereof.
 4. The process according to claim 3wherein said particulate metal sulfide additive comprises iron pyrite.5. The process according to claim 1 further comprising the steps,following the step of treating the sulfided sorbent in the regenerationzone;recovering the active metal oxide sorbent from the regenerationzone; and combining the active metal oxide sorbent with asulfur-containing gas in the desulfurization zone at a temperaturesufficient to allow the active metal oxide sorbent to absorb at leastone sulfur compound from the sulfur-containing gas.
 6. The processaccording to claim 5 further comprising the step of adding freshparticulate metal sulfide additive to said active metal oxide sorbent.7. The process according to claim 2 wherein said contacting step occursat a temperature of between about 650° F. and 1000° F.
 8. The processaccording to claim 1 wherein said oxygen-containing gas in said treatingstep includes an oxygen-containing gas selected from the groupconsisting of dilute, neat, or oxygen enriched air.
 9. The processaccording to claim 2 wherein the particulate metal sulfide additive insaid contacting step is present in an amount less than about 20 percentby weight, based on the combined weight of said sorbent and saidadditive.
 10. The process according to claim 2 wherein the active metaloxide sorbent and the particulate metal sulfide additive of saidcontacting step are supported on a particulate support material.
 11. Theprocess according to claim 2 wherein the active metal oxide sorbent ofsaid contacting step is supported on fluidizable support material andmixed with fluidizable particles of the particulate metal sulfideadditive, and wherein the regeneration zone is defined by a transportbed reactor.
 12. The process according to claim 2 wherein theregeneration zone is defined by a fluidized bed.
 13. The processaccording to claim 2 wherein said active metal oxide sorbent comprisesan active metal oxide selected from the group consisting of zinc oxide,zinc titanate, zinc aluminate, zinc silicate, zinc ferrite, iron oxide,nickel oxide, manganese oxide, cerium oxide, copper oxide, copper ceriumoxide, copper titanate, vanadium oxide, cobalt oxide, tungsten oxide,calcium oxide, calcium carbonate, magnesium oxide, magnesium carbonate,and mixtures thereof.
 14. The process according to claim 2 wherein thesulfur-containing feed stream is a fuel gas and said at least one sulfurcompound is selected from the group consisting of H₂ S, COS, and CS₂.15. The process according to claim 2 wherein said active metal oxidesorbent comprises at least one additive selected from the groupconsisting of promoters and stabilizers.
 16. A process of initiating theregeneration of a sulfided sorbent derived from an active metal oxidesorbent comprising treating said sulfided sorbent with anoxygen-containing gas in a regeneration zone, in the presence of aparticulate metal sulfide additive, at a temperature sufficient toexothermically react the particulate metal sulfide additive with oxygen,to thereby increase the temperature of the regeneration zone to atemperature which initiates the reaction of the sulfided sorbent withoxygen.
 17. The process according to claim 16 wherein the particulatemetal sulfide additive comprises a mineral ore selected from the groupconsisting of iron pyrite, alabandite, bornite, braggite, chalcopyrite,covellite, chalcocite, marcasite, millerite, molybdenite, oldhamite,pyrrhotites, wurtzite/sphalerite, digenite, cubanite,argentite/acanthite, and pentlandite, and mixtures thereof.
 18. Theprocess according to claim 17 wherein the mineral ore is iron pyrite.